This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This is a part of a study done in coordination with the CaNPRC to compare the in vivo infectivity and pathogenicity of a standard stock of SHIV-SF162 P4 developed for the evaluation of vaccine efficacy in macaque models. In this study, we determined the infectivity of SHIV-SF162 P4 in pig-tailed macaques after intravenous inoculation.